Plant Growth Hormones

From the desk of Neutrog’s resident microbiologist Dr. Uwe Stroeher

Spinach treated with Seamungus There are a number of plant growth hormones which are critical to plant development. These hormones do everything from determining the natural shape of the plant, to controlling root development, seed set, ripening of fruit and even distance between nodes.

Most people are familiar with the way sunflowers move to face the sun – this is due to a plant hormone called Auxin or indole-3 acetic acid. In sunflowers, this hormone causes the plant cells to grow more elongated on the side facing away from the sun, meaning that the plant then bends towards the light. This is seen more in younger sunflowers because the hormone level is higher in young plants. It is also generally higher in the tips of plants, and then reduces in the roots.

Varying levels of these hormones is critical, and excessive levels can become an issue. A plant hormone called gibberellin was initially found in a fungus which caused rice plants to fall over – they grew too high and therefore could not support themselves. On the flip side, this hormone has been used to lengthen the nodes in sugar cane leading to increased sugar storage.

Another essential plant hormone is cytokinin, which causes cells to divide – in essence, resulting in growth of plants. This hormone is produced in the roots and then moved via water to the rest of the plant.

In order for plants to grow properly there needs to be a balance between these hormones.  Have you ever wondered why cutting off the main stem of a tree results in it losing its shape? This is because by cutting the tip out where auxins are produced, you unbalance the levels of these hormones so the tree starts to grow shoots more randomly. You also see this imbalance in things like galls – in this case plant pathogenic bacteria that tricks the plant into producing excessive amounts of both auxin and cytokinin, resulting in cancer-like growth on plants.

So how does this relate to soil microbes? There are a number of microbes which actually release plant growth hormones including cytokinin and auxins.   It turns out that bacteria also use auxin or indole-3-acetic acid as a way of communicating, so it has a dual purpose. When you have these bacteria in the soil, they stimulate plant cells to lengthen and divide, thereby increasing root development. 

However, none of this happens if microbes aren’t present in the soil or if you don’t feed them. Ideally, you want to create an environment where plant hormones manufacturing bacteria are growing and secreting these hormones. This can be best achieved by getting that organic matter into the soil, or by using a fertiliser like Seamungus, which feeds both the plants and microbes. Your plants will benefit in no time. Seamungus is a health tonic and planting food for all plants including natives, lawns and bare-rooted roses. It is an ideal winter fertiliser and due to the seaweed element contained in Seamungus, it makes a great soil conditioner. It is my go-to product along with GOGO Juice.

In summary, bacteria can actually influence plant growth by releasing plant growth hormones – it’s just another way good soil microbiology can help your garden. Products such as Seamungus and GOGO juice from Neutrog are available at Bunnings, Mitre 10, Stratco, Home Timber & Hardware and all good garden centres.

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